Carbohydrate structures, exposed on the surface of cells or occurring in soluble form in body fluids, are important in many biological recognition processes. To investigate such processes, low molecular weight oligosaccharides are sometimes not satisfactory. Therefore, a great deal of effort has been devoted to the development of techniques (ref. 1 to 4) for attaching oligosaccharides to larger molecules such as proteins, to give high molecular weight, multivalent conjugates. The obtained "neoglycoproteins" can be used as immunizing antigens to produce carbohydrate-directed antibodies, or as antigens in immunoassays to detect such antibodies.
However, for many applications, it is problematic to use protein conjugates. For example, in immunoassays using carbohydrate antigens, the presence of protein epitopes is highly undesirable. An alternative to proteins in these cases are water-soluble, weakly immunoreactive polymers of the polyacrylamide type. Several reports have recently appeared describing the preparation of oligosaccharide-acrylamide copolymers, both linear (ref. 5 to 14) and crosslinked (ref. 15 to 17). The general strategy for preparation of these conjugates has been to attach an olefinic group to a carbohydrate, and then copolymerize this derivative with acrylamide. The olefinic group has been introduced into the carbohydrate molecule either as an allyl glycoside at an early stage in a synthetic scheme (ref. 5-7, 9-12 and 15), by acryloylation of an amino function of a mono- or oligosaccharide derivative (ref. 8, 11, 13, 14, 17), or by other methods (ref. 16). These known techniques are, however, subject to drawback in that they cannot be directly applied to reducing di- or oligosaccharide reactants, since the reaction conditions necessary result in cleavage of interglycosidic linkages.
Few reports have appeared to date (ref. 14, 18) on the attachment of an olefinic group onto a reducing oligosaccharide. Reducing oligosaccharides of great complexity and structural variety can be isolated from natural sources such as milk (ref. 19), urine (ref. 20), and faeces (ref. 20), and also from chemical or enzymatic hydrolyzates of glycoproteins (ref. 21), glycolipids (ref. 22, 23), or lipopolysaccharides (ref. 24).